feat(crons): Add TickVolumeAnomolyResult

This will be used to pass around the result of anomaly detection during
clock ticks.

Part of #79328

src/sentry/monitors/types.py

@@ -2,6 +2,7 @@
 
 from dataclasses import dataclass
 from datetime import datetime
+from enum import StrEnum
 from typing import Literal, NotRequired, TypedDict, Union
 
 from django.utils.functional import cached_property
@@ -118,3 +119,23 @@ class IntervalSchedule:
 
 
 ScheduleConfig = Union[CrontabSchedule, IntervalSchedule]
+
+
+class TickVolumeAnomolyResult(StrEnum):
+    """
+    This enum represents the result of comparing the minute we ticked past
+    with it's historic volume data. This is used to determine if we may have
+    consumed an anomalous number of check-ins, indicating there is an upstream
+    incident and we care not able to reliably report misses and time-outs.
+
+    A NORMAL result means we've considered the volume to be within the expected
+    volume for that minute. A ANOMALY value indicates there was a drop in
+    volume significant enough to consider it abnormal.
+    """
+
+    NORMAL = "normal"
+    ABNORMAL = "abnormal"
+
+    @classmethod
+    def from_str(cls, st: str) -> TickVolumeAnomolyResult:
+        return cls[st.upper()]